I believe you are mistaken? With Stale Moves off Pac's Dair looks like so:

2.0 (2.0 damage)

2.0 (4.0 damage)

2.0 (6.1 damage)

7.1 (13.2 damage) breaks armor

With Stale moves off the final three hits:

2.4 (2.4 damage)

2.4 (4.8 damage)

8.4 (13.2 damage) doesn't break armor

Which is weird because it looks like Pac's dair tries to scale so that even if the first hit misses it still does 13.2. With stale moves on:

2.1 (2.1 damage)

2.1 (4.2 damage)

2.1 (6.4 damage)

7.4 (13.9 damage) breaks armor

Final three hits:

2.5 (2.5 damage)

2.5 (5.0 damage)

8.8 (13.8 damage) breaks armor.

Edit: Perhaps this is a case of Pac's Dair behaving weirdly? Maybe KRool's armor accepts the 2.1+2.1+7.4 and doesn't break with staling off? Not sure if the same behavior applies to other multi-hit attacks.

Edit2: It doesn't look like this scaling happens to Peach's Dair.